1. Field of the Invention
This invention relates to making splice joints on multiple conductor telephone cables. More particularly the invention relates to a method for preparing a cable to be joined and the method of preparing and using a filled self-curing plastic to make an air tight reinforced plastic splice joint.
2. Description of the Prior Art
Telephone cables vary in diameter depending on the number of individual lines or pairs of lines included inside the cable cover. A typical cable 3.2 inches in diameter contains 2700 pairs of wires. The outer cover or protective layer is typically made of lead extruded on the cable at the time of manufacture. More recently cables have been made with an outer protective cover made of plastics such as polyethylene, polypropylene and polybutylene. All such cables are capable of being installed underground and the joints must be completely sealed and air tight. When such cables are originally installed, the cables must be sealed at the splice joint. When the lines fail or maintenance requires that the cables be opened, the outer layer or cover must be opened to facilitate repairs and then resealed to provide air tightness at eleven pounds per square inch.
Heretofore, lead covered cables which are sealed have been sealed by making lead wiped joints. Such joints are made by covering the open area with a lead plate sleeve wrapped around the open area and then applying molten lead to form a cover which extends from one end of the cable over the lead covered open area to the other end. The hot molten lead forms a molecular bond with lead on the cable and the lead sleeve and would be expected to be superior to the parent cable. If lead wiped joints could be made in a factory and left undisturbed, very few joints would give trouble. In large cities, in and around telephone exchanges and even in large buildings, a very large number of telephone cables are hung or supported adjacent each other on large racks and hangers. To obtain access to a particular cable it is usually required that several cables be moved and bent out of shape. After the particular cable is repaired, the cables must be bent and moved back in place which often causes additional breaks in the existing and just made lead wiped joint. Workmen often climb over such cables and cause stresses in and bending of the repaired cables. It has been found that most leaks and breaks in repaired cables occur at the joint connection where the parent cable enters the splice joint. It is believed that the stiff and enlarged splice joint induces maximum stresses in the adjacent cable and that the hot lead connection to the cold lead cover creates a crystalline cold joint junction subject to breakage when strained.
Not only are lead splice joints subject to easy failure but they are time consuming to make and require special skill on the part of the workmen who work with molten lead and heating devices.
Splice joints made on plastic covered cables are usually only wrapped tape which will not provide a water tight seal between the plastic cover and the material used to close the joint.
Splice joints whether made from hot lead or a plastic material must meet standard underwriting and laboratory tests which are designed to prove the usefulness of the splice joint and/or the splice case used to facilitate making the splice joint. It is believed that no plastic splice joint heretofore proposed has been able to meet the underwriters test for compression, tension and bonding and still maintain a proper seal.